Review and fix CaptureMouse (per Bug 1204 commit comment)

This is using the same idiom of only capturing if not capturing already.  These cases in AutoDuck, Resizing, Grabber and TQP might have been latent ASSERTs.  This based on precedent rather than actual elicited buggy behaviour.

src/effects/AutoDuck.cpp

@@ -862,6 +862,7 @@ void EffectAutoDuckPanel::OnLeftDown(wxMouseEvent & evt)
       for (int i = 0; i < AUTO_DUCK_PANEL_NUM_CONTROL_POINTS; i++)
          mMoveStartControlPoints[i] = mControlPoints[i];
 
+      if( !HasCapture() )
          CaptureMouse();
    }
 }

src/toolbars/ToolBar.cpp

@@ -168,6 +168,7 @@ void ToolBarResizer::OnLeftDown( wxMouseEvent & event )
    mOrigSize = mBar->GetSize();
 
    // We want all of the mouse events
+   if( !HasCapture() )
       CaptureMouse();
 }
 

src/toolbars/ToolManager.cpp

@@ -1358,6 +1358,7 @@ void ToolManager::OnGrabber( GrabberEvent & event )
    }
 
    // We want all mouse events from this point on
+   if( !mParent->HasCapture() )
       mParent->CaptureMouse();
 
    // Start monitoring shift key changes

src/widgets/Ruler.cpp

@@ -2526,6 +2526,7 @@ void AdornedRulerPanel::HandleQPClick(wxMouseEvent &evt, wxCoord mousePosX)
    // Check if we are dragging BEFORE CaptureMouse.
    if (mMouseEventState != mesNone)
       SetCursor(mCursorSizeWE);
+   if ( !HasCapture() )
       CaptureMouse();
 }